In one DNA string there is room for 13 cromosoms.
One string have 13 places, the first, second,3,4,5,6...13.
There is three groups of cromosoms, A,B,C.
The A cromosomes can be placed 1,2,3 or 4 in a row. (there can be more than four on one string but maximum 4 in a row, AND just one row with 4 on one string! But 3rows with three is possible, you know what I mean)(AAABAAABAAACC)
The B cromosomes can be placed 1,2 or 3 in a row. On one string there can be maximum 2 rows with 3 B cromosomes, but of course not after each other BBBBBB.)
The C cromosomes can be placed 1,2 or 3 in a row. On one string there can be maximum 1 row with 3 C.

So, the question is: How many possibilities are there to put a DNA string together?

Accepted examples: AAAABAAACCCBB, BBBAAAABBBCAB...

the only combination that is not valid is the ones with 4A,2x3B and 3C.
example: AAAABBBCCCBBB, BBBAAAACCCBBB...

Need help with this, I don't know the answer, please show how to solve this(Nod)